The present invention relates to a well construction for manholes permitting access to underground conduits, such as water mains, sewer pipe systems, gas mains, conduits containing utility lines such as telephone and electrical lines, and the like.
In underground installations of pipe systems, manholes and appropriate manhole wells ae disposed at predetermined locations along the system for gaining access, for example, to valves, gates, taps, connections and the like for inspection. The top of the access wells is closed with a removable metallic lid, and the wall of the well is sometimes provided with a built-in ladder in the form of steel rungs or steps attached to the wall of the well. The wall itself may be precast of concrete or like material, or made of cast iron, or the like, casing. Alternatively, the well may be made of masonry construction. Whatever the structure adopted for the well construction, the well is generally circular or oval and is provided with an inverted frusto-conical section, having its smaller diameter portion disposed at the top and its widest diameter portion disposed toward the bottom, superimposed on a generally cylindrical portion of a predetermined height disposed at the bottom of the well to provide a working area for maintenance or installation personnel working on the underground system. The narrowest end of the well is normally obturated by a removable manhole cover flush with the pavement or with the ground surface.
A necessary requirement of a manhole well casing is that its wall be capable of supporting without collapsing the side load imposed thereon by the earth in which the well casing is buried. The casing walls and floor or base must be impervious to seepage of water in order to prevent flooding of the well. Furthermore, the floor or base of the well must be relatively sturdy so as to provide a strong support for a person working within the manhole well and, in addition to being impervious to seepage of water and mud through the floor or at the junction between the floor and the casing walls, the base must provide a strong footing for the bottom of the casing walls, and a sturdy support for the conduit or pipe running through the casing.